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DevelopmentSega Master System / Mark III / Game Gear |
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Ultima IV: Quest of the Avatar
Random number generator
RandomNumber:
push de
push hl
; Get stored value
ld hl, (RNGState)
; Multiply by 3
ld d, h
ld e, l
add hl, de
add hl, de
; add low byte to high
ld a, e
add a, h
ld h, a
; set high byte to that
ld (RNGState), hl
; add controller state derived value
ld hl, RNG_ControllerEntropy
add a, (hl)
pop hl
pop de
ret
push de
push hl
; Get stored value
ld hl, (RNGState)
; Multiply by 3
ld d, h
ld e, l
add hl, de
add hl, de
; add low byte to high
ld a, e
add a, h
ld h, a
; set high byte to that
ld (RNGState), hl
; add controller state derived value
ld hl, RNG_ControllerEntropy
add a, (hl)
pop hl
pop de
ret
RNGState is a 16-bit value, seeded with $55aa initially. RNG_ControllerEntropy seems to be a sum of all controller inputs since the start of the game. This function therefore gives some user-influenced random data.
- See the main page for Ultima IV: Quest of the Avatar
